
public class p1004_157ms {

	public static//
	// -----
	// -----
	class Main {
		public static void main(String[] args) throws Exception {
			java.io.BufferedReader reader = new java.io.BufferedReader(new java.io.InputStreamReader(System.in));
			float sum = 0;
			for (int i = 0; i < 12; i++) {
				sum += Float.parseFloat(reader.readLine());
			}
			System.out.printf("$%.2f", sum / 12);
		}
	}

	// -----
	// -----

	public static void main(String[] args) throws Exception {
		Judge.run();
	}

}
